The present invention relates to actuators for use principally with internal combustion engines. More particularly, the present invention relates to hydraulic actuation of actuators, including fuel injectors and camless engine intake/exhaust valves.
A prior art hydraulically actuated, intensified injection system (commonly a HEUI injection system) 10 is depicted in prior art FIG. 1 and consists of five major components:
1. Electronic Control Module (ECM) 20
2. Injector Drive Module (IDM) 30
3. High Pressure actuating fluid supply pump 40
4. Rail Pressure Control Valve (RPCV) 50
5. HEUI Injectors 60
Electronic Control Module (ECM) 20
The ECM 20 is a microprocessor which monitors various sensors 22 from the vehicle and engine as it controls the operation of the entire fuel system 10. Because the ECM 20 has many more operational inputs than a mechanical governor, it can determine optimum fuel rate and injection timing for almost any condition. Electronic controls such as this are absolutely essential in meeting standards of exhaust emissions and noise.
Injector Drive Module (IDM) 30
The IDM 30 is communicatively coupled to the ECM 20 and receives commands therefrom. The IDM 30 sends a precisely controlled current pulse to energize the solenoid of each injector 60. Such energization acts to port high pressure actuating fluid to the intensifier of the respective injector 60. The timing and duration of the IDM 30 pulse are controlled by the ECM 20. In essence, the IDM 30 acts like a relay.
High Pressure Actuating Fluid Supply Pump 40
The high pressure actuating fluid supply pump 40 is a single stage pump and is in the prior art, typically a seven piston fixed displacement axial piston pump and is driven by the engine. The high pressure actuating fluid supply pump 40 draws in low pressure actuating fluid (most commonly engine oil, but other actuating fluids could be used as well) from the reservoir 46, elevates the pressure of the actuating fluid for pressurization of the accumulator or rail 42. The rail 42 is plumbed to each injector 60. During normal engine operation, pump output pressure of the high pressure actuating fluid supply pump 40 is controlled by the rail pressure control valve (RPCV) 50, which dumps excess flow back to the return circuit 44 to the reservoir 46. The reservoir 46 is at substantially ambient pressure and may be at the normal pressure of the lubricating oil circulating in the engine of about 50 psi. Pressures in the rail 42 for specific engine conditions are determined by the ECM 20.
Rail Pressure Control Valve (RPCV) 50
The RPCV 50 is an electrically operated dump valve, which closely controls pump output pressure of the high pressure actuating fluid supply pump 40 by dumping excess flow to the return circuit 44 thence and to the reservoir 46. A variable signal current from the ECM 20 to the RPCV 50 determines output pressure of the pump 40. Pump output pressure is maintained anywhere between about 450 psi and 3,000 psi during normal engine operation. When the actuating fluid is engine lubricating oil, pressure while cranking a cold engine (below 50 degrees F.) is slightly higher because cold oil is thicker and components in the respective injectors 60 move slower. The higher pressure helps the injector 60 to fire faster until the viscosity of the actuating fluid (oil) is reduced.
HEUI Injector 60
Injectors 60 of the HEUI type are known and are representatively described in U.S. Pat. Nos. 5,460,329 and 5,682,858, incorporated herein by reference. The injector 60 includes an intensifier piston and plunger, the actuating fluid acting on the intensifier to pressurize a volume of fuel acted upon by the plunger. The injector 60 uses the hydraulic energy of the pressurized actuating fluid (preferably, lubricating oil) to dramatically increase the pressure of the volume of fuel and thereby to cause injection. Actuating fluid is ported to the intensifier by a valve controlled by a solenoid. The pressure of the incoming actuating fluid from the rail 42 controls the speed of the intensifier piston and plunger movement, and therefore, the rate of injection. The amount of fuel injected is determined by the duration of the pulse from the IDM 30 and how long it keeps the solenoid of the respective injector 60 energized. The intensifier amplifies the pressure of the actuating fluid and elevates the pressure of the fuel acted upon by the plunger from near ambient to about 20,000 psi for each injection event. As long as the solenoid is energized and the valve is off its seat, high pressure actuating fluid continues to translate the intensifier and plunger to continuously pressurize fuel for injection until the intensifier reaches the bottom of its bore.
In the prior art fuel injection system 10, pressurized actuating fluid is used to control the injected fuel quantity by using pressure amplification in the injectors 60. As noted above, a pressure source (pump 40) pumps actuating fluid to a pressure rail 42 (accumulator) where pressure is regulated according to the engine load and speed requirement. The pressure regulation is done via the rail pressure control valve 50 that dumps some of the pressurized actuating fluid to ambient (reservoir 46) in order to maintain the desired pressure in the rail 42.
Prior Art Rail RPCV 50
The RPCV 50 is an electronically controlled, pilot operated valve. The basic components of the RPCV 50 are depicted in Prior Art FIG. 2 and include:
Body 51
Spool valve 52
Spool spring 53
Poppet 54
Push pin 55
Armature 56
Solenoid 57
Edge filter 58
Drain Port 59
The RPCV 50 controls pump outlet pressure of pump 40 in a range between about 450 and 3,000 psi. An electrical signal to the solenoid 57 from the ECM 20 creates a magnetic field which applies a variable force on the armature 56, shifting the poppet 54 to control pressure. With the engine off, the valve spool 52 is held to the right by the return spring 53 and the drain ports 59 are closed.
Approximately 1,500 psi of oil pressure is required to start a relatively warm engine. If the engine is cold (coolant temperatures below 32xc2x0 F.), 3,000 psi of oil pressure is typically commanded by the ECM 20. Initially, pump outlet pressure enters the end of the body 51 and a small amount of oil flows into the spool valve 52 chamber through the pilot stage filter screen and control orifice in the end of the spool valve 52. The electronic signal causes the solenoid 57 to generate a magnetic field which pushes the armature 56 to the right. The armature 56 exerts a force on the push pin 55 and poppet 54 holding the poppet 54 closed allowing spool chamber pressure to build. The combination of spool spring 53 force and spool chamber pressure hold the spool valve 52 to the right, closing the drain ports 59. All oil is directed to the pressure rail 42 until the desired pressure is reached.
Once the engine starts, the ECM 20 sends a signal to the RPCV 50 to give the rail pressure desired. The injection control pressure sensor 22 monitors actual rail pressure. The ECM 20 compares the actual rail pressure to the desired rail pressure and adjusts the signal to the RPCV 50 to obtain the desired rail pressure. The pressure in the spool chamber is controlled by adjusting the position of the poppet 54 and allowing it to bleed off some of the oil in the spool chamber through the drain port 59. The position on the poppet 54 is controlled by the strength of the magnetic field produced from the electrical signal from the ECM 20. The spool valve 52 responds to pressure changes in the spool chamber (left side of the spool) by changing positions to maintain a force balance between the right and left side of the spool. The spool valve 52 position determines how much area of the drain ports 59 are open. The drain port 59 open area directly affects how much oil is bled off from the outlet of the pump 40 and directly affects rail pressure in the rail 42. The process of responding to pressure changes on either side of the spool valve 52 occurs so rapidly that the spool valve 52 is held in a partially open position and outlet pressure of the pump 40 is closely controlled by venting a significant volume of the actuating fluid out the drain ports 59 under certain engine operating conditions, primarily at the lower engine load conditions. The RPCV 50 provides for substantially infinitely variable control of pump outlet pressure between 450 psi and 3,000 psi.
In the prior art, injection pressure is controlled with the electronically controlled pressure-regulating valve, RPCV 50, as noted above. The hydraulic supply pump 40 is deliberately selected to provide excess output to ensure that the rail 42 is sufficiently supplied with actuating fluid at the highest demand conditions of the engine (full load conditions). The RPCV 50 valve relieves high oil pressure to tank 46 (ambient) to maintain desired pressure in the rail 42 at all engine conditions when the maximum actuating fluid is not required. Typically, engines operate under full load only a very small percentage of the total operating time. This results in significant wasted pumping energy, which has a significant negative fuel economy effect on the engine. Further, during the injection event, the flow consumption rate of the injector 60 exceeds greatly the instantaneous pump flow recovery and causes large pressure drops in the rail 42. There is therefore a need to better control fluid pressure in the fuel injection high-pressure rail 42 and compensate for large instantaneous fluid flow requirements by the injectors 60.
The regulating valve of the present invention substantially meets the aforementioned needs. The regulating valve minimizes the pressure drop in the rail caused by injection events and the time for pressure recovery. Effectively, the regulating valve advantageously lessens the requirements of oil displacement by both the high-pressure pump and rail size. Ultimately, the regulating valve of the present invention advantageously improves the stability of the fuel injection system (shot-to-shot and injector-to-injector variability).
The regulating valve of the present invention stores oil at a low pressure during the pressure regulating cycle rather than discharging it to ambient as in the prior art. The low-pressure oil is then used to pressurize oil in the rail during the injection event. The flow-recovery regulating valve replaces the prior art injection pressure regulator valve, RCPV 50.
The instant regulating valve is built on the principles of an RCPV with the addition of a dual acting piston and low-pressure relief. The main control spool of the RCPV is modified to allow a low-pressure to vent scheduled transition during flow recovery. The dual acting piston is responsible for the flow recovery. The low-pressure relief allows storage energy in the dual acting piston that is then made available to the rail 42 as needed by the actuators (injectors 60).
The main contributions of the regulating valve of the present invention are:
(a) increase the pressure recovery rate in the fuel injection high-pressure oil rail following an injection event;
(b) decrease the pressure drop in the rail due to the injection event;
(c) minimize the fluid volume requirement for the rail; and
(d) minimize the displacement requirement of the high pressure pump.
Items (a) and (b) above directly affect the stability of shot-to-shot and injector-to-injector performance of the fuel injection system. Item (c) improves the package of the fuel injection system by minimizing the physical size of the rail installed in an area of the engine in which many engine components compete for a very limited space available. Item (d) improves the power output of the engine by lessening the power draw from the high pressure pump.
The present invention is a pressure control valve assembly for controlling fluid pressure to an actuator (such as fuel injectors or camless hydraulic actuators), the pressure control valve assembly being in fluid communication with an actuating fluid pump and being disposed intermediate the actuator and the pump. The invention includes an energy storage component, the energy storage component acting on a certain volume of actuating fluid under pressure, the stored energy being selectively releasable to the actuator for augmenting the actuating fluid pressure in the actuator. The present invention is further a method of control.